As is known, lysozymes and especially lysozymes of animal origin, are compact polypeptides with a hydrolase activity [E.C.3.2.1.17], with a net positive charge and with a molecular weight of about 15,000. Slight differences in the polypeptide chain in the number of amino acid residues do not substantially change the biological activity of the enzyme. The lysine residues present in the chain vary from a minimum of 6 in egg white lysozyme to a maximum of 8 in dog lysozyme.
As is well known, any chemical treatment which leads to the loss of the basic feature, such as acetylation, inactivates the enzymes. The presently held opinion is that the .epsilon.-amino groups of lysine must preserve their basic nature in order that the total biological activity of the molecule is preserved or is only slightly modified. If a chemical transformation results in an increase in the basicity, some of the biological properties may, in theory, be improved.
Animal lysozymes are reasonably stable at acid pH values but unstable at alkaline pH values; they are heat-resistant for some minutes in weakly acidic media, without an appreciable loss of enzymatic activity, this heat stability being due to the number of cystine residues present in the molecule.
From a purely enzymatic point of view, the substrates for enzyme activity of the animal lysozymes are bacterial cell wall mucopeptides and animal and plant chitin: for this reason, they have also been called N-acetyl-muramide glycanohydrolases.
Biologically, lysozymes have a lysing activity on many bacteria, inducing release from the cell walls of immunologically competent amino sugars. In higher organisms, the lysozymes form part of the natural cell and/or humoral immunity systems or, more precisely, of the antibody-completement-properdin system.
That the role of the lysozymes is not limited solely to immune activity and bacterial lysis is suggested by the fact that animals under sterile conditions have the same lysozyme activity at a humoral level as animals under non-sterile conditions. A transglycosylase and a transferase activity has, in fact, been observed which is particularly useful, for example, in the regenerative processes of connective tissues.
The in vivo methylation processes of some amino acids are generally related to specific enzymatic control processes, after genic transcription.
We have found that it is chemically possible to achieve the trimethylation of the lysine contained in the lysozyme polypeptide chain to give the new substance .epsilon.-N-trimethyl[lys]-lysozyme.